A wireless communication base station is disclosed, configured to serve a plurality of user terminals in a series of downlink radio frames wherein user terminals in a first group are served in a first temporal region of the downlink radio frame and user terminals in a second group are served in the second temporal region of the downlink radio frame. In order to be able to connect high-strength sheets or other sheets which can be difficult to weld to each other, the sheets are connected in the connecting region by a strip-shaped fastening element. The alignment offset determination may include: forming a data field of four measured symbols around the detected phase difference; searching for the position of a two-symbol window in the data field that maximizes a phase difference; and calculating the alignment offset from this position.